The present invention relates generally to a control system and a control method for an appliance. More specifically, the present invention relates to a control system and a method for determining a working profile for a cooking/heating appliance such as a cooking range. The control system is configured to measure the line voltage for the cooking/heating appliance and to adjust a working profile and/or load outputs of the cooking/heating appliance accordingly.
In different geographic areas within the U.S. as well as among various countries throughout the world, the nominal line voltage can differ significantly. The typical nominal line voltage is 208V, 220V, or 240V. However, the actual voltage can vary from the nominal line voltage. In resistive loads such as electrical cooking/heating elements used in cooking/heating appliances, relatively large load output changes can occur with relatively small changes in the line voltage since load output varies with the square of the voltage. Similar load output changes can occur with non-resistive loads such as electric motors for washing machines, or inverter circuits for induction cooktops.
The performance of an appliance can be negatively influenced by the deviations in the line voltage. For example, if a cooking range is designed for operation with a line voltage of 240V, but is used in an area where the line voltage is 208V, the difference in line voltage will have a negative impact on the cooking performance of the cooking range with respect to pre-set cooking profiles
Rather than designing a different control system for each different nominal line voltage, it would be desirable to provide a single cost effective control system for an appliance. Such a control system would allow the appliance to be used with a variety of line voltages. To be attractive for such applications the control system should either automatically adapt to the applied line voltage, or at least be readily and simply pre-settable to various line voltages in the factory or during installation. For example, if a cooking range is able to sense that 208V is being supplied on the power line, it can adjust pre-set cooking profiles/parameters so that they are specifically tailored to the lower voltage (208V) operation, thereby providing uniform cooking results independent of the difference in the line voltages. FIGS. 5, 6 and 7 illustrate how the control may be adapted to different voltages by altering the duty cycle of the relays for different conditions in accordance with the principles of the invention.
In addition, it would be desirable to provide a control system for an appliance which automatically compensates for over-voltage or under-voltage conditions without any apparent difference in the performance of the appliance, thereby preventing damage to the appliance and/or avoiding a potential safety hazard, all without interrupting the use and enjoyment of the appliance.